Apparatus for mechanically expanding large diameter pipe

ABSTRACT

Apparatus for expanding pipe in increments includes a plurality of expandable dies having a length substantially less than that of the pipe. Each die includes a first curved outer section with a radius substantially equal to the inside diameter of the expanded pipe, a second curved outer tapered section having a minimum radius no greater than the inside radius of the unexpanded pipe, and a third arcuate section tangent to the first and second sections. The third section is also arcuate in its longitudinal direction and has a radius sufficiently long to prevent stressing of the fibers of the pipe wall a substantial amount beyond the yield point of the pipe material.

United States Patent [72] Inventor Douglas E. Alexander {56] References Cited a? y"??? Township UNlTED STATES PATENTS estmore an ounty. a. [Zn App]. NO. 818,036 2,780,271 2/1957 Ewart et a1 72/399 [22] Filed Apr. 21, 1969 Primary Examiner-Charles W. Lanham [45] Patented Mar. 23, 1971 Assistant Examiner-MichaelJ. Keenan [73] Assignee United States Steel Corporation Attorney-Martin J. Carroll ABSTRACT: Apparatus for expanding pipe in increments includes a plurality of expandable dies having a length substantially less than that of the pipe. Each die includes a first curved outer section with a radius substantially equal to the inside [54] CZ Z E EQ Q EK ESE EXPANDING diameter of the expanded pipe, a second curved outer tapered 3 Cl 6D section having a minimum radius no greater than the inside aims rawmg radius of the unexpanded pipe, and a third arcuate section tan- [52] US. Cl 72/393, gent to the first and second sections. The third section is also 72/399 arcuate in its longitudinal direction and has a radius suffi- [51] Int. Cl B2ld 41/02 ciently long to prevent stressing of the fibers of the pipe wall a [50] Field of Search 72/393, substantial amount beyond the yield point of the pipe materi- 394, 399, 400, sv l s iol si, 317, 415

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PATENTEDMRNIBYI $572,081

sum 1 OF 2 INVENTOI? DOUGLAS E. ALEXANDER Attorney PATENTEUMARNIQ?! $572,081

SHEET 2 [IF 2 INVENTOR DOUGLAS 6'. ALEXANDER Attorney APPARATUS FOR MECHANICALLY EXPANDING LARGE DIAMETER PIPE This invention relates to apparatus for mechanically expanding large diameter pipe and more particularly to an im provcmcnt in the apparatus shown in Ewart et al. U.S. Pat. No. 2.780.271 dated Feb. 5. 1957. The apparatus shown therein, which expands the pipe in relatively short increments, has accomplished most of the objects for which it was designed. However. there is a slight wrinkling or corrugated effect at the connection between increments which is particularly noticeable when the pipe is coated. This detracts from the overall appearance of the pipe and results in customer complaints.

It is therefore an object of my invention to provide mechanical pipe-expanding apparatus in which the wrinkling or corrugated effect between increments of expanded pipe is minimized or eliminated.

These and other objects will be more apparent after referring to the following specification and attached drawings, in which:

FIG. 1 is a longitudinal section of the pipe expander with which my invention is used;

FIG. 2 is a fragmentary transverse section taken on the line 11-11 of FIG. 1;

FIG. 3 is a fragmentary transverse section taken on the line III-III of FIG. 1;

FIG. 4 is a fragmentary top plan view of the forward end of the die assembly showing the radial keys;

FIG. 5 is a schematic view of an expander segment of my invention within a pipe being expanded; and

FIG. 6 is an enlarged view of a pipe section between expanded and unexpanded portions of the pipe.

Referring more particularly to the drawings, reference numeral 1 indicates an expander unit for expanding a pipe P. An hydraulic cylinder 3 having a piston 54 therein is spaced from expander unit I in axial alignment therewith. A piston rod 4 is connected to piston 54. Conveyor rollers 5 support and convey the pipe P to and from the expander unit 1. The expander unit 1 includes a hollow expandable die assembly 8, into the rearward or left end thereof is drawn a tapered polygonshaped mandrel 9 attached to piston rod 4 so as to expand the die assembly against pipe P. A fixed thrust plate 10 is secured to the forward end of the die assembly 8 and serves to align and brace the assembly during the expansion operation.

The die assembly 8 consists of a plurality of circumferentially disposed dies 11. each die being generally wedgeshaped and formed with a generally curved outer surface 12, which is adapted to be in contacting relation with the inner surface of the pipe P to be expanded, and a flat tapered inner surface 13 against which a corresponding surface of the tapered mandrel 9 is adapted to slide as the mandrel drawn into the die assembly.

A portion of the curved outer surface 12 of each die 11 adjacent the rearward end of the die assembly is provided with a slight inward taper. The portion of the pipe P encircling this tapered portion of the dies 11 is partially expanded during the expansion operation to provide a tapered connection between the fully expanded and unexpanded portions of the pipe. As the pipe P is moved forward on the expander unit 1, the partially expanded portion of the pipe is disposed circumjacent to the forward portion of the die assembly 8 to provide an area of overlap and is fully expanded in the next expansion increment.

The outer surface 12 of the uppermost die in the assembly may be formed with a longitudinal slot 14 which extends the length of the die and is adapted to receive the longitudinal seam weld of the pipe P.

The forward end 19 of each die 11 is in contacting relation with annular thrust plate 10 and is formed with a radial keyway 20, FIG. 4, which is adapted to slidably cooperate with one of a series of radially disposed thrust plate keys 21 which are secured to thrust plate 10 by bolts 22.

By virtue of the keys 21, dies 11 are radially aligned with the permanently positioned thrust plate 10, and, while the dies are permitted to move radially outward during the expansion, rotary motion of the dies is prevented. In addition, the radial keys prevent longitudinal movement of the dies when mandrel 9 is retracted from the die assembly.

To secure thrust plate 10 against movement during the expansion operation, the forward surface thereof is attached to annular flange 23 of piston rod housing 24.

In operation, with the dies 11 collapsed, the end of pipe P is moved to surround the expander unit 1. The dies 11 are then expanded to expand an increment of pipe length after which the dies are collapsed and the pipe P moved forwardly toward cylinder 3 and another increment of pipe length expanded by expanding dies 11. The operation is repeated until a little more than one-half of the pipe length is expanded when the pipe is withdrawn and the other half then expanded. The operation and the parts described are old in the Ewart et al. patent and thereference numerals used are also those of the Ewart et al. patent. Other details of the machine can be obtained from the Ewart et al. patent.

My invention relates to the shape of the expander die segment 11 as shown in FIG. 5. It will be understood that the die shown has a curved outer surface as shown in FIGS. 2 and 3 and that it is the longitudinal shape of the die which is the subject of my invention. The outer surface of the die is divided into three sections; a first section 11a having a radius substantially equal to the inside radius of the expanded pipe, a tapered second section 1117 having a minimum radius no greater than the inside radius of the unexpanded pipe, and a curved connecting section between and substantially tangent to the sections Ila and 11b. I have found that the corrugated effect between increments of expanded pipe can be minimized or eliminated by making the radius R of the connecting section sufficiently long to prevent stressing of the inner and outer fibers of the pipe wall beyond the yield point of the pipe material. This may be determined by the following equation:

where E modulus of elasticity of the pipe material, I yield strength stress of the pipe material and t wall thickness of the expanded pipe.

From FIG. 6 it will be seen that are A at the neutral axis of the pipe wall I in section He has no strain, that the compressive strain S, (inches/inch) at the inner are of the pipe wall t and the tensile strain S at the outer arc of the pipe wall are equal in magnitude, that R (in inches) is the minimum allowable longitudinal radius of section 110 which will produce no plastic strain or stress beyond the yield point in the outer fibers of the pipe wall, and that Tis the angle (in radians) subtended by the radius R through a unit arc length A.

Equation l is arrived at as follows:

Yield Strength Stress (Y) Assume that it is desired to obtain a 30 inch outside diameter pipe with a maximum wall thickness of 0.562 inch by expanding 1.25 percent a pipe having an outside diameter of 29.630 inches which is made from steel having a yield strength stress of 52 l03 and a modulus of elasticity of 30Xl0. From Equation l 2X52X10a =162 Inches.

Since the radius R for this type of material varies only with wall thickness a die of the proper size having a minumum radius R of 162 inches may be used with any diameter tube having a maximum wall thickness of0.562 inch.

The axial length (TL) of tapered section 11b is dependent upon the arc length of section 11c and may be obtained from Equation (7) eR(1-cos P) TL Tan P where e offset between the expanded and unexpanded portions of the pipe or the difference in radii, R is the longitudinal radius, and P is the angle of taper. The taper angle P is equal to the angle subtended by radius R for the full length of section 110. For pipes of about 30 inch diameter l have found that the length of section llc should be about inches. From Equation S =gg; ig or .00173 in./in. and from Equation (4), T= =00616 radians or 021. Hence While one embodiment of my invention is shown and described, it will be apparent that other adaptations and modifications may be made without departing from the scope of the following claims.

lclaim:

1. Apparatus for mechanically expanding pipe in increments comprising a plurality of dies having a length substantially less than the length of the pipe to be expanded and arranged about a central axis; and means for expanding said dies radially against the inside of said pipe to expand the same; each of said dies in expanded position including a first elongated transverse curved outer section having a radius substantially equal to the inside radius of the expanded pipe, a second elongated transverse curved outer tapered section having a minimum radius no greater than the inside radius of the unexpanded pipe, and a connecting transverse curved outer section between and substantially tangent to said first and second sections; the connecting section of each die being arcuate in its longitudinal direction with its radius being sufficiently long to prevent stressing of the inner and outer fibers of the pipe wall a substantial amount beyond the yield point of the pipe material.

2. Apparatus according to claim 1 in which the minimum radius of the longitudinal arc of the connecting portion of the die is substantially equal to where E modulus of elasticity of the pipe material, l= yield strength stress of the pipe material and l wall thickness of the expanded pipe.

3. Apparatus according to claim 1 in which the minimum radius of the longitudinal arc of the connecting portion of the die is equal to percent of where E modulus of elasticity of the pipe material, Y yield strength stress of the pipe material and t wall thickness of the expanded piper 

1. Apparatus for mechanically expanding pipe in increments comprising a plurality of dies having a length substantially less than the length of the pipe to be expanded and arranged about a central axis; and means for expanding said dies radially against the inside of said pipe to expand the same; each of said dies in expanded position including a first elongated transverse curved outer section having a radius substantially equal to the inside radius of the expanded pipe, a second elongated transverse curved outer tapered section having a minimum radius no greater than the inside radius of the unexpanded pipe, and a connecting transverse curved outer section between and substantially tangent to said first and second sections; the connecting section of each die being arcuate in its longitudinal direction with its radius being sufficiently long to prevent stressing of the inner and outer fibers of the pipe wall a substantial amount beyond the yield point of the pipe material.
 2. Apparatus according to claim 1 in which the minimum radius of the longitudinal arc of the connecting portion of the die is substantially equal to where E modulus of elasticity of the pipe material, Y yield strength stress of the pipe material and t wall thickness of the expanded pipe.
 3. Apparatus according to claim 1 in which the minimum radius of the longitudinal arc of the connecting portion of the die is equal to 80 percent of where E modulus of elasticity of the pipe material, Y yield strength stress of the pipe material and t wall thickness of the expanded pipe. 